The present invention relates to an X-ray CT system and image processing method. More particularly, the present invention is concerned with an X-ray CT system and image processing method for producing second tomographic images, which represent sections different from sections represented by first tomographic images, using the first tomographic images produced from projection data.
Known as a modality for producing tomographic images are X-ray computed tomography (CT) systems that irradiate as radiation, for example, X-rays, detect X-rays having passed through a subject, and produce tomographic images through calculation.
The X-ray CT system includes an X-ray source and an X-ray detector array opposed to the X-ray source with a subject between them. The X-ray detector array detects X-rays irradiated from the X-ray source to the subject. The X-ray CT system scans the subject by rotating the X-ray source about the subject and moving the X-ray source. This results in a plurality of views of projection data of the subject. The X-ray CT system recomposes the acquired projection data so as to produce tomographic images of a predetermined slice thickness representing sections at predetermined positions of the subject.
In general, the X-ray CT system produces tomographic images of sections orthogonal to the direction of a body axis linking the subject's head and the subject's tiptoe. The tomographic images are called axial images.
On the other hand, the produced axial images may be subjected to image processing again in order to produce images of difference sections. More specifically, numerous axial images are superposed on one another in order to reconstruct planar images extending in any direction. Thus, new planar images are produced. The image processing is performed as separate handling. After all axial images are reconstructed, different planar images are produced. Therefore, much time is required until the produced planar images are used for diagnosis. In many cases, after a user diagnoses a lesion using axial images, the image processing is performed if necessary.
For the above reason, there is a demand for an X-ray CT system capable of readily performing the image processing.
Known as such an X-ray CT system includes an X-ray CT system in which as soon as an axial image (body-axis transverse image) of one section is reconstructed, data items lying on a predetermined plane parallel to the body axis are sampled from the image, interpolated, and rearranged (refer to, for example, Patent Document 1). This processing is performed on a plurality of axial images. When radiography for producing axial images is completed, images of sections parallel to the body axis are also produced.
In the above X-ray CT system, an extra scan need not be performed in order to produce new tomographic images. However, X-ray CT systems capable of producing tomographic images are on the trend toward faster scanning and a larger number of detector arrays. There is therefore a possibility that the X-ray CT system described in Patent Document 1 may have to produce a much larger number of images.
[Patent Document 1] Japanese Examined Utility Model Publication No. 6-44405